Breast cancer can cause armpit pain when it occurs and the cancer cells are shed and can invade the surrounding lymphatic vessels and metastasize to their local lymphatic drainage areas.
Initially, patients mostly present with swollen lymph nodes in the ipsilateral armpit, with the enlarged lymph nodes still mobile. Subsequently, the lymph nodes become smaller and more numerous, and eventually fuse together and become fixed.
As the disease progresses, metastatic lymph nodes can be felt in the supraclavicular and contralateral axillae and may be painful to the touch.
In addition, localised pain in the patient’s armpit is not necessarily due to breast cancer, but can also be considered as an enlarged axillary lymph node due to ligament damage or regional infection; or breast enlargement, which is caused by the patient’s pain radiating to the armpit.